Heatwave: Why is Heathrow so hot? Temperature exceeds 40C in London

Heathrow often records temperatures higher than the rest of the UK.

Seren Morris | London Evening Standard | 19 July 2022

The UK recorded its highest temperature on record, exceeding 40C, amid the heatwave this week. Heathrow hit 40.2C at 12.50pm on Tuesday, according to provisional Met Office figures.

Heathrow often records temperatures higher than the rest of the UK - but not for the reason most of us may think.

We may assume that Heathrow is so hot because the airport's tarmac runways absorb heat, while CO2 is generated by the planes flying in and out of the hub every day.

But, according to experts, these factors barely impact the temperature and are not the reason why Heathrow is often so much hotter than the UK.

Why is Heathrow so hot?

Heathrow gets so hot because of the urban heat island, which is the process where cities and buildings absorb and retain more heat than the surrounding rural areas.

This is why cities are generally hotter than rural areas and towns.

Heathrow's tarmac runways and airport buildings form an urban heat island, but so do other surrounding areas.

During the heatwave in 2019, the BBC reported that the average Heathrow temperatures are typically the same, if not very similar to, the temperatures of Kew, which is eight miles away.

On Tuesday, by 11am, when the temperature had exceeded 35C in parts of London, it hit 36.9C at Kew Gardens and 36.6C at Heathrow.

Surprisingly, the CO2 expelled by the planes at Heathrow doesn't make much of a difference to the area's temperature.

Paul Williams, Professor of Atmospheric Science at the University of Reading, told the BBC that the CO2 warms the entire climate rather than one specific area, because of how it spreads in the air.

He said: "If you measure the CO2 levels above Heathrow they wouldn't be any higher than other parts of the UK because it spreads so quickly."

Additionally, Heathrow is hotter than other areas in the UK because of its distance from the sea. Typically, areas further inland tend to be hotter because they don't get the cooling effect that coastal areas do.

So there are a number of reasons why Heathrow experiences high temperatures - but it's not just about the planes and runways.